Initial testing using RouterStats Lite produced an interesting graph which appears to
show the frequent loss of DSL that I was originally complaining to BT about.
The first test of only 50 minutes duration shows no less than 13 drops.
Can you confirm that this is abnormal line behaviour before I launch a further salvo at BT?
Before contacting Demon, it may be worth posting the statistics and graphs on some web space, then posting the link here for people to review first, before contacting Demon.
If you are losing sync 13 times in an hour, that is a fault - you should be able to hold sync for several weeks on a reasonable line. Ideally you'd be testing in a BT NTE5 test socket to eliminate your wiring completely, but you don't have that option. If a BT engineer comes to your house as part of fault finding, ask him or her to replace your existing master socket with an NTE5 - they will probably do that anyway, but it never hurts to ask. You can then move your filter to the BT NTE5 - though keep the faceplate as you will need it if you fit the VDSL interstitial filter in the future.
If the ADSL fault is resolved without an opportunity to have a BT NTE5 fitted, contact your phone provider to ask about having one fitted. It will probably be free of charge, and will give you a test socket for future troubleshooting.
Demon aren't, in my opinion, the ISP they once were after all the takeovers. I was with them from 1996 until the ScottishTelecom days, when ntl (as it was then - it later became part of Virgin Media) launched cable modem service in my area and I could get a faster connection without the horrific ISDN call costs I was incurring. Eventually, the BT exchange was upgraded to support ADSL and the quality of the ntl cable modem service had deteriorated, so we moved from ntl to Zen ADSL in 2004. I'm still with Zen, though our cabinet was enabled for FTTC last month and we upgraded earlier this month.
At one point, Demon's technical support was excellent. I'm not sure how good they are now. If you don't get the backup you want, consider moving - there are excellent ISPs out there with UK based support centres at various price points. The more expensive ISPs (such as Zen, AAISP and IDnet) tend to be more persistent over faults
When on Zen ADSL, I had problems with a sizeable drop in sync speed and disconnections that was down to water in a joint. Twice, BT did a pair swap and closed the fault, but it was not resolved. Each time, I contacted Zen who re-opened the fault (it did not affect voice, so I had to go via Zen rather than my phone provider, BT Retail). The third engineer checked all the joints and found the joint in the underground DP where our drop cable connects to the D-side was waterlogged. The engineer disassembled and dried out that joint, replaced the crimps on our line, and everything was back to normal.
Ultimately, every ISP are at the mercy of BT Openreach, but if Demon refuse to persist with your problem, consider moving ISP. Even if you don't move ISP now, this is a good reminder to eliminate your dependence on ISP provided e-mail addresses and web space, so that you can move freely in the future.